How much is beneficial seems highly variable. If you have a diet high in omega-6 fatty acids (nuts, seeds, legumes, conventionally raised animal products, esp conventional eggs), to keep a reasonable balance of omega-3 to omega-6, you'd need more omega-3s than someone who gets a lot of their fat from different sources that are more saturated or monounsaturated. And some people who are working on health issues who likely have long-term imbalances seem to do well on fairly high doses.

This guy recommends limiting polyunsaturated fat (omega-3 and omega-6 are forms of polyunsaturated fat) altogether--keeping a good ratio, but altogether a small portion of fat intake.

We take Dr. Mercola's Krill Oil. The dosage is 1,000 mgs which provides 90/epa 50/dha ~ we love it. Supposedly it's higher in phospholipids than other fish oils which increases the bioavailability of the omega-3s,and improves the omega-3 to omega-6 ratio so you actually need less.